The presence of chloride ions in the electrolyte affected the electrodeposition behavior of CdTe from the ammoniacal basic electrolyte of pH 10.7, and changed the properties of the resulting CdTe layers. The photo-assisted effect, that is, the increase in the deposition rate under the irradiation of white visible light onto the growing surface of the CdTe, was depressed in the chloride electrolyte. A set of cyclic voltammograms for basic electrolytes containing only Cd (II) or Te (IV) ions suggested that the chloride ions depress the reduction of not Cd (II) ions, but Te (IV) ions. The deposit prepared from chloride electrolyte was slightly Cd-rich CdTe containing additional phases, such as elemental Cd and Cd3Au. The measurements of the reflectivity spectra and the electrical property suggested that the CdTe electrodeposited from the chloride electrolyte is a complicated compensated semiconductor, because chlorine atoms substituted for Te atoms in CdTe crystals formed some impurity levels in the band gap of CdTe.
Selective recovery of copper, zinc and nickel from electroplating wastewater was studied by investigating the sulfuration behaviors of these metal components and the filtration characteristics of the metal sulfides produced. As model metal solutions, CuSO4, ZnSO4 and NiSO4 aqueous solutions of 100mg/dm3 initial concentrations were employed. Three kinds of sulfurating agents : sodium sulfide (Na2S), sodium disulfide (Na2S2) and sodium tetrasulfide (Na2S4) of 6.8×10−2mol/dm3 were used. For selective sulfuration of CuSO4, ZnSO4 and NiSO4, the sulfurating agent was added to the metal solutions, adjusting the pH of these solutions at pH=1.4-1.5, 2.4-2.5 and 5.5-6.0, respectively. As a result, it was found that Na2S was most effective for selective sulfuration of copper, zinc and nickel. The sulfuration behaviors of copper, zinc and nickel in electroplating wastewater were almost the same as those in model solutions. Furthermore, the filtration characteristics such as the average specific filtration resistance and the compressibility coefficients of the metal sulfide produced with different sulfurating agents were measured. It was recognized that the average specific filtration resistance of the metal sulfides produced with different sulfurating agents was different. It was also found that the compressibility coefficient of the metal sulfides was lower than that of metal hydroxide. The compressibility coefficient of the metal sulfides decreased in the order of Na2S, Na2S2 and Na2S4.
The corrosion resistance of Zn-Mg alloy plated steel prepared by the electrodeposition from 1-ethyl-3-methylimidazolium bromide (EMIB) based ionic liquid was investigated in 5mass% NaCl aqueous solution at 35ºC. The first red rust generation time of Zn-Mg alloy plated steel containing more than 2.5mol% of Mg was about 20 weeks independently of the Mg content. The corrosion resistance of Zn-Mg alloy plated steel was about 20 times higher than that of Zn plated steel. The excellent corrosion resistance of the Zn-Mg alloy plating is due to the fact that the fine and insulating initial corrosion product ZnCl2•4Zn(OH)2•H2O is formed on the Zn-Mg alloy plating and Mg suppresses the cathodic reaction of corrosion and the formation of ZnO, which causes the corrosion of plating and steel. As a result, the effect of sacrificial protection of the Zn-Mg alloy for steel continues for a long time, and the corrosion resistance is improved.